Analysis of a blood sample generally seeks to determine:                the total number of leucocytes;        more specifically, the number of leucocytes by sub-populations (basophils, eosinophils, neutrophils, monocytes and lymphocytes);        the number of erythrocytes and platelets; and        the haemoglobin level.        
Several analysis techniques are known, in particular:
assay of the haemoglobin is carried out after lysis of the erythrocytes, i.e. the destruction of the membrane of the cells of erythrocytes, and by measurement by spectrophotometry of the haemoglobin released in the medium; the assay of the haemoglobin also requires the stabilization of the haemoglobin in a complexed form (oxyhemoglobin or cyanmethemoglobin) in order to measure the absorbance of a single compound at the appropriate wave length.
total leucocyte count is carried out on the blood sample by resistivity with specific lysis of the erythrocytes and protection of the leukocytes.
differentiation of the leucocytes and the counting thereof by sub-population is carried out:                either by resistivity volumetric measurement after specific lysis of the erythrocytes, protection of the leucocytes and adjustment of the pH; this however does not allow differentiation of all the sub-populations in a single analysis;        or by optical way, in particular by flow cytometry; after specific lysis of the erythrocytes and protection of the leucocytes, by measuring different parameters (in particular diffraction, fluorescence, absorbance), on a flow of leucocytes in the axis of the narrow, medium and wide angles and optionally after addition of a labelling agent (for example chlorazol black, or a DNA or RNA labelling dye, or a fluorescent dye) and by measuring at different wave lengths; this technique allows differentiation of the sub-populations of leucocytes.        
the erythrocyte and platelet count is carried out on a diluted sample without the addition of specific reagent by resistivity measurement.
Numerous automatic blood cell analyzers exist which use these techniques in order to obtain a blood sample analysis which is as complete as possible.
In these automatic apparatuses, two different analysis circuits traditionally coexist:                a first circuit designed to measure the haemoglobin and/or the total leucocyte count; and        a second circuit designed to carry out on the blood sample the differentiation and/or a leucocyte count by flow cytometry.        
Each circuit is characterized by a dilution rate of the blood sample suited to the measurement means used, the addition of one or more reagents and appropriate means for implementation and measurement.
Thus, for the measurement of haemoglobin and the counting of the leucocytes, the circuit typically comprises a so-called counting tank in which the blood sample is diluted, a reagent in particular comprising the lysis compound of the erythrocytes, the stabilisation compound of the complex formed from the haemoglobin and the leucoprotective compound is added to it, and the following are measured directly in this cell: haemoglobin by spectrophotometry and the number of leucocytes by resistivity. The dilution rate is chosen so that the analysis solution is perfectly homogeneous and so that the detection apparatus is not saturated. This dilution rate is comprised between 1/100th and 1/500th, generally between 1/160th and 1/180th.
For leucocytic differentiation by flow cytometry, the circuit uses a tank for dilution of the blood sample to which one or more reagents containing an erythrocyte lysis agent, optionally a differentiation agent (for example a DNA or RNA leucocyte fluorescent dye) are added, then a fraction of this solution is taken in order to inject it into a flow-through optical tank of a flow cytometer. The dilution rate used here is less than 1/100th, allowing an optimal analysis time to be obtained with the cytometers currently available on the market (of the hydrofocus type).
Thus, conventionally at least two different reagents must usually be used for the two analysis circuits and two different dilutions of the blood sample are carried out in these two analysis circuits.
The main objectives of manufacturers are to simplify the existing automatic apparatuses by reducing the number of components and reagents, allowing reduction of the production and maintenance costs and the size of the automatic apparatuses, without however reducing the time of a complete blood sample analysis.
The present invention in particular aims to achieve these objectives.
Document WO 2004/003517 for this purpose proposes a method and equipment in which the two analysis circuits have means in common. The principle is to carry out a first dilution of the blood sample in a single dilution tank and to successively transfer fractions of selected volumes of this dilution to a measuring or counting unit, in order each time to measure or count different elements contained in the blood sample. In order to carry out a complete analysis, namely counting the erythrocytes and platelets, counting the leucocytes, measurement of the haemoglobin and leucocytic differentiation, the document describes the following solution: using a first transfer to count the erythrocytes and platelets, adding a lysis agent to the dilution tank, then carrying out a second transfer to count the leucocytes, carrying out a third transfer of lyzed dilution solution to measure the haemoglobin level, adding a leucocytic differentiation reagent, and carrying out a fourth transfer to realize the leucocytic differentiation in the measuring unit.
This principle may allow the use of a single so-called dilution tank, but it does not allow a saving of analysis time because the measurements or counting are carried out successively after each transfer of a fraction of the dilution. Moreover, it requires perfect control of the successive volumes of reagents and diluents transferred to the measuring unit. Moreover it also requires the use of several syringes and lysis reagents.
The objective of the present invention is also to overcome such drawbacks.